This invention relates to ignition systems for internal combustion engines and more particularly, to controlling ignition timing to eliminate engine knock.
In recent years, there have been many modifications to automobile engine systems. These include the addition of components such as emissions control components and catalytic converters as well as changes in gasoline formulations which eliminate lead and affect octane ratings. One by-product of these changes is a condition prevalent in many automobiles called "knocking". This phenomena is caused by improper ignition of fuel in engine cylinders and causes severe pounding against side wall of the cylinders. One way to eliminate knocking is to retard the ignition timing for the engine. Various schemes to adjust or retard engine timing are shown, for example, in U.S. Pat. Nos. 4,061,116; 4,106,447; 4,130,096; 4,211,194; 4,233,944; 4,236,491; 4,243,007; 4,243,008; 4,249,494; 4,257,364; and, 4,275,692.
Typically, the various systems employed use some type of sensor or method for detecting a knock condition, manipulating the signal generated by the engine's ignition system and supplying this manipulated signal to the ignition coil which fires the spark plugs to combust the mixture in the engine cylinders. Two areas of concern in implementing any of these various schemes involve prevention of damage to the ignition coil and also responsiveness of the retarding circuitry to engine operation at higher rpm's (6,000 rpm and up). It is particularly important to disconnect the circuitry manipulating the signal from the ignition system from the ignition coil when the engine is not running in order to eliminate current drain and prolong the life of the coil. One way of doing this is shown in the Borst et. al. U.S. Pat. No. 4,088,106 which uses a counter, a speed related signal and a clock. The circuitry is designed to sense when the engine is operating at very low speed or has stopped in order to open a switch controlling current flow through the ignition coil. While the above described circuitry will disconnect current flow to the ignition coil, thus preventing current drain through the system, additional circuit components are required in addition to those already utilized to retard ignition timing.